The epoxidation of propene with hydrogen peroxide in the presence of an epoxidation catalyst is usually carried out with a molar excess of propene relative to hydrogen peroxide in order to avoid hydrogen peroxide decomposition and to achieve high selectivities for propene oxide. Epoxidation of propene with a heterogeneous titanium silicalite catalyst is known from EP 0 100 119 A1. Epoxidation of propene with a homogeneous manganese catalyst is known from WO 2011/063937. Epoxidation of propene with a homogeneous tungstophosphate catalyst is known from U.S. Pat. No. 5,274,140.
For an efficient use of propene, non-reacted propene has to be recovered from the reaction mixture of the epoxidation reaction and recycled to the epoxidation reaction. Commercial propene grades usually contain propane as an impurity due to the manufacturing processes used for making propene. Since the epoxidation catalysts used for epoxidizing propene have little or no activity for oxidizing propane, the use of a propene grade containing propane in an epoxidation process with a propene recycle will lead to accumulation of propane in the process. Efficient recycling of propene then requires a separation of propane from propene and a purge of propane from the process.
WO 2005/103024 discloses the use of a conventional C3 splitter column for separating propane from a mixture of propene and propane recovered from an offgas from an epoxidation process before recycling the propene to the epoxidation. Such a conventional C3 splitter column has to be operated with a high reflux ratio which leads to a high energy consumption.
WO 2004/018088 discloses recovery of propene and propane from a gaseous propylene oxide process purge stream by absorption in liquid propane followed by separation in a C3 splitter column, providing an overhead vapor stream containing 31.2% by weight propene and 65.2% by weight propane which is recycled to propylene oxide production. However, due to the high propane content in the recycle stream this method leads to a high accumulation of propane in the process that requires considerably larger equipment for the epoxidation reaction and the reaction mixture workup and increases energy consumption in the reaction mixture workup.
Therefore, there is still a need for a process for the epoxidation of propene with hydrogen peroxide in which a propene starting material containing propane can be used and propane can be purged from the process with less equipment and energy consumption.